1. Field of the Invention
The present invention relates to a navigation apparatus that acquires a trace of a vehicle and learns an unregistered road (which is a road not stored in a map data storage medium). The present invention also relates to a method and a computer program product for a navigation apparatus.
2. Description of Related Art
A navigation apparatus having a road learning function is known (e.g., see JP-H6-88733A). According to such a navigation apparatus, when a vehicle travels on an unregistered road (which is a road not stored in a map storage medium), the navigation apparatus acquires a trace of a vehicle traveling on unregistered road and records the trace in unregistered road storage means through converting a data format of the trace, so that the converted trace and the road map data stored in the map storage medium have the same data format. When the vehicle travels again an area having the unregistered road, the navigation apparatus displays the unregistered road on a road map together with a present position mark indicative of an estimated position of the vehicle.
The inventor of the present application has found that the navigation apparatus described in the JP-H6-88733 involves the following difficulties. When it is determined that a vehicle travels on an unregistered road, there is a possibility that a vehicle makes a turn in direction by traveling on an empty lot adjacent to a road, and a trace of the vehicle on the empty lot is recorded as unregistered road in the unregistered road storage means. As seen from the above, since such an unneeded path can be recorded and accumulated in the unregistered road storage means, accuracy of learning an unregistered road may be disadvantageously low.